[SPARK-9316] [SPARKR] Add support for filtering using `[` (synonym for filter / select)

Add support for
```
   df[df$name == "Smith", c(1,2)]
   df[df$age %in% c(19, 30), 1:2]
```

shivaram

Author: felixcheung <felixcheung_m@hotmail.com>

Closes #8394 from felixcheung/rsubset.